This invention, in general, relates to refrigeration and heating systems and in particular to an improved thermostatic expansion valve for use in refrigeration systems.
In a compression refrigerating system the refrigerant, in a gaseous state, is compressed and then passed into a condenser where it is cooled, condensed, and accumulated as a liquid. This liquid refrigerant, now at a higher pressure, flows into the inlet port of an expansion valve which has an outlet port conducting fluid to an evaporator. The expansion valve is generally a spring-loaded pressure reducing valve which allows the refrigerant to pass therethrough at a rate predetermined to maintain a given evaporator pressure. This reduction in pressure causes the refrigerant to evaporate in an evaporating coil. The resulting heat of vaporization is transfered to air, water, or any other fluid flowing over the evaporator coil.
Expansion valves, thus, are used in refrigeration and air conditioning systems as control devices which restrict the flow of liquid refrigerant as it passes from the condensor to the evaporator. Essentially, expansion valves control the flow of liquid refrigerant so that it arrives at the evaporator at a uniform rate consistent with the heat transfer capability of the evaporator coil. Such expansion valves fall generally into two categories, that is, fixed orifice devices, and variable orifice devices. In addition, variable orifice devices are usually classified as either automatic valves, or thermostatic valves such as the valve herein.
Thermostatic valves are the subject of such commonly owned U.S. Pat. Nos. 2,786,336 and 3,742,722, and 3,738,573. Essentially, as disclosed in such patents, expansion valves are spring loaded in one direction. This limits their use in bi-directional or reverse flow valves. However, in some refrigeration and air conditioning systems., such as heat pumps, it is necessary to provide for reverse refrigerant flow. If any of the known expansion valves, such as those referred to hereinbefore are used in such systems it is necessary to modify the system to permit their use. Even then, in the reverse direction additional superheat must be generated to overcome the spring force and the reverse closing force caused by the pressure difference. In addition, modified systems are not only cumbersome, but usually more expensive.
In commonly owned U.S. Pat. No. 4,852,364 the system modification problem was overcome by the provision of an expansion valve incorporating a built-in check valve. This valve overcomes the problems of the prior art, but it is still subject to two disadvantages. It includes additional working parts, and two complete expansion valves are required for use in a heat pump system. If a conventional expansion valve is used as a bi-directional valve, and in its normal operating direction of flow it controls flow at a superheat substantially different than it does in the reverse direction.
By the practice of this invention both of these disadvantages are overcome in a manner not disclosed in the known prior art.